1. Field of the Invention
The present invention relates to an engine start controller having a starter motor for starting an engine by using a battery as power source, and more specifically to an engine start controller that is suitable to start the engine in a situation where an electrical control unit (ECU) for controlling the engine start becomes inoperative due to a temporary voltage drop of the battery which is caused at the engine start.
2. Description of the Related Art
As to engine start controllers that start engines by driving the starter motors installed in vehicles, a well-known controller is provided with a power source control ECU for performing the drive control of the starter motor and an engine ECU that carries out the drive control of the engine (see, for example, Unexamined Japanese Patent Application No. 2006-183613). An engine start controller of this type is suitable especially when the engine start controller has a smart ignition system.
The smart ignition system conducts ID check of a vehicle and a key by wireless. If the ID is matched, the system starts the engine in response to the driver's pressing an operation unit (starter switch) such as a press-button switch that is disposed in a vehicle compartment. The smart ignition system is also called Push Start System.
An engine start controller of this type improves operationality. On the other hand, in a situation where a battery with decreased capacity is used to start the engine, the battery voltage is transiently reduced due to a high current that flows into the starter motor. As a result, the ECU of the engine start system becomes inoperative, which occasionally disables the engine to start.
In order to solve the inoperativeness of the ECU of the engine start system, the engine start controller disclosed in the above-mentioned publication is designed so that a lower limit of operating voltage of the power source control ECU is set lower than a lower limit of operating voltage of the engine ECU. Even if the battery voltage is temporarily reduced lower than the operating voltage of the engine ECU when the starter motor is driven while the battery capacity is decreased, the engine can be started as long as the battery voltage is maintained at such a level that allows the power source control ECU to properly operate.
The engine start controller of the publication, however, requires to install the power source control ECU for implementing the drive control of the starter motor, separately from the engine ECU, detect the operation of the engine ECU by using the power source control ECU, and preliminarily maintain a detection result in the power source control ECU. In addition, the lower limit of operating voltage of the power source control ECU has to be set lower than that of the engine ECU for ensuring startability. Consequently, the controller described in the publication raises the concern that costs may be high. Also, its complicated structure causes a high incidence of malfunctions.
Moreover, if an improper operation of a CPU, such as microcomputer constructing the ECU, leads to a wrong judgment that the starter switch is pressed (constant ON state of a register), the engine might be improperly started.
One possible way to solve these problems is to form the configuration from the starter switch to the ECU of the engine start system into a redundant configuration.
However, the engine start controller with a redundant configuration has a complicated structure, and therefore increases costs.